$(a)$ What is the direction of magnetic field lines inside a bar magnet and outside of it?
$(b)$ What does the degree of closeness of the field lines represent?

$A$ magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected if the current in the wire is increased? Support your answer with a reason.

$A$ student performs an experiment to study the magnetic effect of current around a current-carrying straight conductor with the help of a magnetic compass.
He reports that:
$(i)$ the degree of deflection of the magnetic compass increases when the compass is moved away from the conductor.
$(ii)$ the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
Which of the above observations of the student appears to be wrong and why?

State the rule to determine the direction of magnetic field produced around a current-carrying conductor.

Name and state the rule to determine the direction of a force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it. Name a device that uses a current-carrying conductor and a magnetic field.

On which principle does an electric bell work?